Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $63.57   3.228%   $65.622   $65.62   $65.60   $65.60  
  Purchase #2 $181.45   13.123%   $205.2617   $205.26   $205.25   $205.30  
  Purchase #3 $57.61   7.545%   $61.9567   $61.96   $61.95   $62.00  
  Purchase #4 $151.92   9.674%   $166.6167   $166.62   $166.60   $166.60  
  Purchase #5 $202.63   7.608%   $218.0461   $218.05   $218.05   $218.00  
  Purchase #6 $89.89   7.179%   $96.3432   $96.34   $96.35   $96.30  
  Purchase #7 $188.47   8.105%   $203.7455   $203.75   $203.75   $203.70  
  7 purchase totals = $935.54       $1,017.5919   $1,017.60   $1,017.55   $1,017.50